The present invention is directed to a method and apparatus for the production of thin films produced from liquids that undergo phase transition to a viscoelastic state such as polymers and resins which have been dissolved or melted, the liquids are placed onto a substrate and the substrate is rotated in a manner and under such conditions that a uniform thin film is produced which can be readily removed from the substrate. Such thin films can serve as samples for analysis by infrared spectroscopy or as carrier vehicles for samples to be analyzed by infrared, x-ray fluorescence (xe2x80x9cXRFxe2x80x9d) or other spectrographic methods and the like.
Films made in accordance with the present invention can also be used as standards for calibration of Infrared and FTIR spectrophotometers and carrier films suitable for XRF can also be used as calibration standards for XRF spectrophotometers.
The formation of coated substrates is known in the art. In this technology, a coating material is prepared in the form of a coating liquid and then adhered to a substrate in a manner and under such conditions that the coating remains affixed to the substrate. For example, Hiroyoshi U.S. Pat. Nos. 5,238,713 and 5,116,250 disclose a coating apparatus including a spinning chuck rotatably supported within an enclosure which holds a substrate. The substrate is a semi-conductor wafer or glass and the coating material is typically a photoresist masking material. The purpose of applying the coating material to the substrate is to form a permanent bond therebetween (i.e. to mask portions of the semi-conductor).
The coating operation is performed by applying a liquid coating material to the top surface of the semi-conductive substrate which is being continuously rotated at high speeds. The liquid coating material is typically applied by a nozzle or other dispensing device. The liquid coating material is typically applied under continuous flow conditions and then drawn outwardly by rotating the table upon which the substrate rests at high speeds. The process relies upon centrifugal force to spread the coating material outwardly to form a coating layer which strongly adheres to the substrate. Such coatings are applied to protect the substrate (e.g. semi-conductor wafers and glass) by remaining permanently bonded thereto.
The present invention is directed, not to producing an adherent coating on a substrate, but rather to producing a thin film that may, if required, be readily removed from the substrate. Such thin films can be used, for example, as optical samples for infrared spectroscopy or as carriers for XRF, infrared and other forms of spectroscopy. The conditions under which the film is made make use of both centrifugal force and centripetal force and thus the process clearly distinguishes from those processes, like the references mentioned above, which produce adherent coatings on substrates.
The present invention is specifically directed to methods and apparatus for forming a thin film on a substrate which film can be easily removed so that it may be used as a sample and/or a medium for spectroscopy. When used as a sample for spectroscopy, the thin film must be optically transmissive in the spectral region of interest. When used as a carrier or medium, the film must be non-absorbing or neutral so that it is not detected by the spectrophotometer in the region where the sample is absorbing or detected.
In another aspect of the invention, the thin films can be used as calibration standards for XRF and other spectrophotometers. In another aspect of the present invention, films of polymers can be used as calibration standards for IR spectrophotometers.